What's the Purpose of Underscores Before Function Names in Go Struct Tags?

Go Struct Tags with Underscores Before Function Names

In Go, struct fields can be annotated with struct tags to provide additional information to the compiler or external tools. However, the use of underscores before function names in struct tags, as seen in the example below, can be confusing.

type CustomLabel struct {
    core.QObject

    _ func() `constructor:"init"`
    _ string `property:"text"`
}

These underscores indicate blank fields. They cannot be referenced directly, but they affect the struct's memory layout. In this case, they are used for alignment purposes.

Blank fields can be used to align subsequent fields to specific memory positions or to match the data layout of another system. This allows for efficient transfer of data to and from other systems in one step.

Note: While blank fields can be beneficial in certain situations, they should be used sparingly as they add unnecessary overhead to all instances of the struct even though they cannot be referenced.

For a comprehensive overview of struct tags, refer to the question "What are the use(s) for tags in Go?"

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